1. Field of the Invention
The invention relates to the preparation of beverages or the like from an extraction material contained in a capsule, for example ground coffee. It relates in particular to a pierceable capsule as a portion pack and to a method for the production thereof.
2. Description of Related Art
Extraction devices for preparing beverages or the like from an extraction material present in a portion pack are known, for example, as coffee or espresso machines and continue to enjoy increasing popularity. In many corresponding systems, the portion packs are formed as capsules in which the extraction material is, for example, closed off in an airtight manner. For the extraction, the capsule is pierced from two opposite sides. On the first side, extraction liquid—generally hot water—is introduced. On the second side, the extraction product is discharged from the capsule. Depending on the beverage to be prepared and the system, a considerable pressure, for example of 5-20 bar, may thereby prevail in the interior of the capsule.
Such capsules must not be confused with—and have to meet entirely different requirements than—portion packs of filter coffee, which are opened by pulling off a foil, removing a cover or the like and are not at any time exposed to an increased pressure. They are equally not comparable to the outer, aroma-tight packagings of “filter pads”. In brewing modules of coffee machines, capsules of the type described here are often passed through horizontally or vertically by the hot brewing liquid and, as mentioned, are thereby exposed to a considerable pressure inside. This also gives rise to the problem of sealing; after all, the pressurized brewing liquid must not get past the capsule and enter the discharge device directly.
Aluminum and plastics, for example polypropylene, have become known in particular as capsule materials. Aluminum capsules keep the extraction material fresh for a long time, but use considerable energy for their production. Polypropylene capsules are advantageous with respect to energy consumption and disposal, but impose increased requirements on the piercing mechanism.
Particularly advantageous with respect to material consumption are deep drawn capsules, which however always have a decidedly conical form.
Available on the market are both, capsules with integrated filtering means and capsules that merely comprise a shell around the extraction material, and for which the piercing mechanism therefore has to be designed in such a way that extraction material is not undesirably discharged from the capsule together with the extraction product.
An example of a capsule without integrated filtering means is disclosed for example in EP 1 886 942.
Available capsules are generally rotationally symmetrical and comprise a peripheral collar, which has a threefold function essential for them to work properly:                the collar serves for closing the capsule during the filling operation, in that it comprises an energy director for ultrasonic welding at a sufficient distance from the interior space of the capsule or a sufficiently large surface area for thermal welding;        the collar serves for holding the capsule before the brewing operation;        the collar is essential for the sealing during the brewing operation, as it ensures that no brewing liquid gets past the capsule and directly enters the discharge device.        
In the case of capsules according to the prior art, an additional sealing function may be assumed by the conical form, which fits very exactly into a corresponding receptacle of the brewing chamber.
Many of the available capsules are shaped in the form of a cup, i.e. they are rotationally symmetrical about an axis and conical. Often, the cover of the cup-shaped capsule is of a different material composition than the actual cup that forms the lateral surface and the bottom surface. Therein, the injection of the extraction liquid takes place through the cover or the bottom surface and the discharge of the extraction product correspondingly takes place through the bottom surface or the cover respectively. This form of capsule has proven successful, both with regard to the mechanical stability and with regard to technical aspects of production.
A particularly problematical issue involves the swirling of the extraction material during the brewing process. During the extraction process, liquid flows through the capsule at high speed. If there is limited compaction of the extraction material, it is made to swirl considerably during the brewing process. For this reason, it has already been proposed (EP 1 886 942) that the extraction material is compressed vigorously during the capsule filling process. However, this method is rather complex, and the pellet-like consistency of the extraction material achieved by the compression can be lost during the transportation of the capsule.
A further problematical issue that is often discussed in connection with portion capsules for brewed beverages is the complex packaging, which adversely affects the energy balance.